1. Field of the Invention
The present invention relates to drivers for a pulsed diode light source, and more particularly to drivers for a pulsed diode light source suitable for improved temperature range operation.
2. Description of Related Art
Pulsed laser diode drivers typically are used to generate pulses of current into one or more laser diodes. Pulsed laser diode drivers are manufactured and sold by a variety of companies, including OptiSwitch Technology Corporation of San Diego, Calif., USA; Analog Modules, Inc. of Longwood, Fla., USA; Avtech Electrosystems Ltd. of Ogdensburg, N.Y., USA; and Directed Energy, Inc., an IXYS Company, of Fort Collins, Colo., USA.
FIG. 1 shows one type of pulsed laser diode driver in which a linear pass element 130 such as a field effect transistor functions as a current driver in a series circuit with a voltage regulated power supply 100 and a laser diode load 120. The linear pass element 130 is part of a linear current source which includes a current sensing element 140 and an error amplifier 150. The current sensing element 140 is placed in the series circuit such that the voltage which develops across the current sensing element 140 is in proportion to the amount of current being conducted through the laser diode load 120. The error amplifier 150 compares the voltage which develops across the current sensing element 140 with a control voltage that is applied at terminal 160 to indicate the desired laser diode current, and adjusts the current conducted by the linear pass element 130 to maintain a constant current. A capacitor 110 is connected across the power supply 100 to provide adequate energy storage so that the delivered pulse keeps the linear current source operating within its linear regime.
The characteristics of capacitors are affected by temperature, which can adversely impact the ability of the driver to maintain a constant current through the laser diode load. The impact on current level can be reduced by using large capacitor banks and operating the linear pass element close to saturation. Unfortunately, the use of large capacitor banks increases the size, weight and bulkiness of the driver, which may be undesirable in some applications.